The invention relates to a shut-off device comprising a single-part housing insertable in a pipeline, and a butterfly valve swivellable by a drive shaft wherein said butterfly valve in its closed position is sealed off from the housing and from the pipe connection, by a distensible entropy-elastic annular seal of U-shaped cross section to which fluid can be applied, with said annular seal being held by a backup ring on a face of the housing.
In a known shut-off valve of this type according to DE 195 42 568 C2 the exterior region of the backup ring which engages the U-shaped cross section of the interior region of the annular seal, is interspersed with drill holes for admitting self-sealing screws, and is removably attached by means of said screws and attached to the face in the set-off of the housing and at its area of the external circumference of the housing sealed off with an O-ring against the set-off in the pipe housing, so as to provide a fluid-proof seal. However, despite undeniable advantages of this shut-off device during various changes of the backup ring with the ring seal, it has been shown that the O-ring adheres very badly to the housing, by suction, on the area of the external circumference of the backup ring. This makes it considerably more difficult to remove the backup ring even after the self-sealing screws have been undone and removed. Furthermore, the expense of using the self-sealing screws turns out to be a disadvantage because even when only one screw is not tight, the fluid acting on the annular seal can escape outwards at that position.
Furthermore, DE-OS 15 000 181 discloses a shut-off device of the type mentioned above, which, due to the selection of the cross section and materials disclosed therein, provides a sealing ring which is extremely difficult to produce, because its external area is to be relatively rigid and inelastic, while the middle interior region which comprises a sealing surface, is to be relatively elastic. Overall, a complicated annular seal made from an entropy-elastic material, a rigid ring and a backup ring are disclosed for providing a seal in a single-part housing. There is no information on how to attach the backup ring. This can only mean that during installation in the single-part housing the backup ring is either pressed against the sealing ring by being fastened in the flange of the pipeline (which results in leakages) or said backup ring is mounted as a shrink ring in the housing. In any case, repairing a faulty sealing ring requires expert personnel who will need to know the entire design and the fluid-carrying pipes of this shut-off device. If such a shut-off device is used in a medium stream with abrasive particles or crystals, the entropy-elastic annular seal wears relatively quickly, and thus needs to be replaced with a new one. For this purpose, the entire shut-off device needs to be de-installed from the respective pipeline and returned to the manufacturer who then needs to remove the faulty annular seal and replace it with a new one. Such repair work is not only time consuming and costly, but also associated with a disadvantage in that a new shut-off device (kept in stock) will have to be placed in the pipeline if waiting for repair of the de-installed shut-off device and the associated downtime is to be avoided.
U.S. Pat. No. 1,844,641 discloses a non-generic shut-off device which comprises a two-part housing with ring flanges on each end, together with which, said housing is inserted in a pipeline. The two housing halves are mutually fastened via a ring with an entropy-elastic annular seal, using screws, and rigidly interconnected by straining screws and shrink rings, thus forming an annular internal set-off. Undoing such a multi-part housing kept together by straining bolts and shrink rings, as well as changing the ring with its entropy-elastic annular seal, can only be undertaken by expert personnel. For this reason, either the entire shut-off device has to be sent to the manufacturer for repair, with downtime extending until the repaired part has been returned, or a new shut-off device has to be used which again increases operating costs.
DE 38 74 059 T2 discloses a non-generic shut-off device which does not comprise a backup ring. Instead, its entropy-elastic annular seal with two facing projections encompasses the interior region of the housing so as to provide a seal, with a central drive shaft of the butterfly valve penetrating said housing. On both ends, said drive shaft must provide a fluid-proof seal not only against the medium flowing in the pipeline, but also against the fluid used for distending the entropy-elastic annular seal. Any exchange of this annular seal necessitates expert personnel because neither sealing the drive shaft after removal and re-insertion, nor removal and replacement of a faulty annular seal with a new seal, can be undertaken by general support staff. Therefore, this shut-off device too, has to be sent to the manufacturer for repair, with downtime extending correspondingly until the repaired part has been returned, or a new shut-off device has to be used which again increases operating costs.
Based on this state of the art, it is thus the object of the invention to provide a shut-off device of the type mentioned above, whose entropy-elastic annular seal, in the case of a leakage, can be repaired quickly and easily by removal together with the backup ring, without creating further sealing problems, thus significantly reducing downtime of the respective pipeline.
In conjunction with the generic notion mentioned in the introduction, according to the invention this object is met in that by means of two annular projections the annular seal engages one annular groove each in each face of the backup ring; in that each of the lateral external areas of said annular seal comprises an integrated projecting sealing ring, and in that the backup ring, in its area situated outside the annular seal, is attached to the housing by means of several conventional hexagon socket screws. The special design of the annular seal with the two facing projections, in conjunction with the projecting sealing rings, integrated into each of the lateral external areas of said annular seal, obviates the need for a set-off in the face of the respective housing. Instead, the backup ring can now be placed together with the annular seal on a plane face of the housing and can be connected with said housing, using conventional hexagon socket screws. Other countersinkable screws can be used as a substitute for such hexagon socket screws.
Because of the sealing rings integrated in the annular seal at the two lateral external areas, there is no longer any need for the hitherto necessary self-sealing screws for attaching the backup ring to the housing. This not only simplifies installation and deinstallation of the backup ring and the annular seal, but it also makes the procedure much faster. Moreover, there is no longer any fixation by suction of one of these annular seals, as is frequently the case with the use of the O-ring used according to the nearest state of the art.
According to a particularly advantageous improvement of the invention, the cross-sectional shape of the facing annular projections matches the cross-sectional shape of the accommodating annular grooves, and in that region, on the two lateral external areas, the projecting sealing rings are arranged. As a result of the excess of the two projecting sealing rings in relation to the lateral external areas, after tightening of the hexagon socket screws and thus of the backup ring at the housing as well as after inserting and tightening the shut-off device within a pipeline, these two sealing rings also press the two annular and facing projections of the annular seal into their annular grooves, thus providing an O-ring like seal. In this way, both an external seal against the fluid flowing through the pipeline, and an internal seal against the fluid distending the entropy-elastic annular seal, are achieved. To this purpose, it is advantageous if the sealing rings integrated in each of the lateral external areas comprise a cross section which is in the shape of a semicircle or a segment of a circle.
According to an advantageous improvement of the invention, the backup ring comprises a fluid pressure chamber at its internal circumferential area; said fluid pressure chamber being in the shape of an encompassing annular groove, with a fluid connection pipe, which is sealed so as to be fluid-proof towards the external atmosphere, directly leading into said annular groove so that pressure can be exerted on the annular seal. This fluid connection pipe comprises a conventional screw connection which for sealing purposes either comprises a sealing metal ring or an adhesive. Unlike the situation with the nearest state of the art according to DE 195 42 568 C2, the fluid connection pipe is not routed through the housing but instead directly from the area of the external circumference, radially into the backup ring. Thus this obviates the need to provide a seal with an O-ring, at the area of the external circumference of the backup ring, as has hitherto been the case. Each of the two annular projections of the annular seal, said projections facing each other, engages an annular groove at the face of the backup ring. Consequently, as a result of pressure being exerted onto these backup rings, by the projecting sealing rings, arranged at the lateral external areas, said sealing rings acting as O-rings, the entire pressure chamber space is simply and very effectively sealed off, for distension of the annular seal, so as to be fluid-proof both towards the external atmosphere and towards the interior of the pipeline.
To further simplify installation and deinstallation, the backup ring is placed on the matching face of the housing, and encompassed by centring turned grooves only in the two diametrically opposed regions of the lead-through of the shaft of the butterfly valve. These centring turned grooves cannot be done without because the lead-through for the shaft of the butterfly valve requires that from the two diametrically opposed regions the housing be widened correspondingly. Advantage of this widening is now also taken for centring the backup ring with its in-between regions in relation to the housing. After centring the backup ring, it can simply be directly attached to the housing, with the distensible annular seal, using conventional hexagon socket screws. There is no longer any need for all-round centring in the form of a pronounced set-off.
At its face pointing away from the annular seal, the housing is sealed off from the end of the pipeline, in a manner known per se, by an O-ring inserted in an annular groove.
To protect the entropy-elastic annular seal and thus to prolong its service life, the butterfly valve is swivelled into and out of its closed position without touching the annular seal. It is only after it has reached the closed position that the butterfly valve is distended, and it is depressurised before it is swivelled out of its closed position. In this way, during the closing procedure with the butterfly valve, the annular seal moves into its closed position without establishing contact and thus with low friction, because the application of pressure to the annular seal occurs only after this. Likewise, the butterfly valve is opened only when the annular seal is without pressure. In both cases, there is a small circumferential clearance between the area of the external circumference of the ring seal and the area of the external circumference of the butterfly valve, both during and after the sealing process.